Sign Language Interpreters are trained professionals who convey messages between two different languages, typically spoken English and American Sign Language (ASL).
Real-Time Captioners are trained professionals who provide a speech-to-text translation which can be read visually on a laptop, computer monitor, or other display screen in real-time.
Media Captioning is captioning of prerecorded multimedia that contains an audio component (i.e. presentations through videos, DVDs, the Internet, and other sources).
Described Media features an audio narration of what occurs visually in a video.